1. Field of the Invention
The present invention relates to a high precision positioning apparatus for positioning a recording medium with respect to an optical system in a holographic storage device with high accuracy, and more particularly, to a high precision positioning apparatus for accurately positioning a recording medium by roughly positioning the recording medium and then minutely moving the roughly positioned recording medium.
2. Description of the Related Art
Conventionally, as storage devices for a computer or the like, there has been widely used magnetic or optical recording media in which information is two-dimensionally written and/or from which information is two-dimensionally read. Examples of known magnetic storage devices include a floppy (registered trademark) disk, a hard disk, and so on, and examples of known optical storage devices include a compact disc (CD), a digital versatile disk (DVD), and so on. In order to meet demand for storage devices having a larger storage capacity, a remarkable advance in the recording density has been made hitherto. Also, development of storage devices using the principle of a hologram (hereinafter, referred to as holographic storage devices) is underway as means for realizing a further increased storage capacity.
A holographic storage device stores information on a hologram, which is formed by causing interference between encoded object light and reference light on a recording medium. Object light is radiated onto a recording medium in the form of two-dimensional digital data, and only reference light is radiated onto the recording medium when information is reproduced. Accordingly, a need arises for accurately positioning the optical system and recording medium of the object light and reference light. Such positioning is carried out by moving a flat-plate shaped recording medium in an in-plane direction while fixing the optical system in place. An example of such a holographic storage device is described in Patent Document 1.
[Patent Document]
Japanese Unexamined Patent Application Publication No. 2001-93157.
The conventional holographic storage devices that have been widely used are card- or disk-type recording media. In the case of a card-type recording medium, each slider is provided in each of the X and Y directions and the recording medium is moved with respect to the optical system using each slider so that the recording medium can be moved in mutually orthogonal X and Y directions in a plane thereof. In the case of a disk-type recording medium, a motor is coupled to the center of the recording medium for moving the recording medium in its circumferential direction, and a slider traversing the motor is provided for moving the recording medium in its radial direction.
However, the positioning apparatus of recording media in the conventional holographic storage device has the following drawbacks.
In order to randomly access data, a recording medium required to be largely moved in units of pages forming holograms. Meanwhile, in order to accurately position the recording medium with respect to the optical system, minute adjustment in positioning the recording medium is required. To perform minute movement, stepping of a driving motor or slider should be performed in a microscopic manner. If rough movement is performed on such driving system, a large load is undesirably applied to the system. In other words, it is difficult to make the rough movement of a recording medium compatible with the minute movement thereof, which results in high cost of the recording medium positioning apparatus.